Geological Society of London. 235 



Prof. Tennant observed that Mr. Sheppard hfid years ago brought horn e sapphires 

 from the same district. They were obtained from the beds of rivers. 



Col. Jenks gave some further statements with regard to the depth to which the 

 corundum-veins referred to in his paper have been worked, and stated that some of 

 the crystals obtained from the veins could be broken across by a very slight pressure 

 in the fingers when first taken from the vein, but that they became hard by exposure 

 to the air. 



IL— March 11th, 1874.— John Evans, Esq., F.E.S., President, in 

 the Chair. — The following communications were read : — 



1. " On the Relationship existing between the Echinothwidce, 

 Wyville Thomson, and the PerischoecJiinidce, McCoy." By R. 

 Etheridge, Esq., jun., F.G.S. 



In this paper the author referred in the first place to the peculiar 

 characters of the genera Calveria and PJiormosoma, Wyville Thom- 

 son, and especially to those in which they approach the Cretaceous 

 genus Echinothuria, S. P. Woodward, and which led Prof. Wyville 

 Thomson to include these three forms in his group Echinothuridee. 

 He remarked that an overlapping of the interambulacral plates, 

 more or less like that occurring in these three genera, is met with 

 also in ArchcBocidaris, McCoy, and Lepidechinus, Hall, belonging to 

 the group of Palseozoic Eciiini which McCoy proposed to call 

 PerischoechinidEe, and which is characterized by the presence of 

 more than three rows of plates in the interambulacral areas. As 

 there is no overlapping of these plates in the other genera referred 

 to this group, it includes two types of structure. The author then 

 discussed the characters presented by the test in the genera of the 

 Perischoechinidaa (namely ArchcBocidaris, PalcecMnus, Perischodomus, 

 Lepidechinus, Eocidaris, Melonites, and Oligoporus), and pointed 

 out that although we have no conclusive evidence of the presence 

 of membranous interspaces along with the overlapping plates in 

 ArchcBocidaris, the fragmentary condition in which the remains of 

 that form ai'e usually found would lead us to infer their existence. 

 No known Palaeozoic genus exhibits the want of distinction between 

 the ambulacra and interambulacra on the ventral half of the test 

 seen in the recent genus Pkormosoma. In Melonites and Oligoporus 

 the author described an increase in the number of rows of plates in 

 the ambulacra, and he indicated that all the Perischoechinidse differ 

 from the later Echini by the increased number of perforations in 

 the ocular and genital plates. 



Discussio:^. — Mr. Etheridge described Calveria as resembling an elastic ball rather 

 than an ordinary Sea-urchin, its calcareous plates being held in place by a flexible 

 membrane, and as connecting the ordinary forms with Eehinothuria, in which the 

 plates slide over one another like armour. He remarked that the apical disks vary 

 in each genus ; in the Pala3ozoic genera the ovarian plates have three or more, and 

 the ocular plates two, perforations. The interambulacral areas in the Palaeozoic 

 genera have invariably more than two rows of plates. In Archceocidaris the plates 

 have bevelled edges. The chief point of the paper was its indicating that a type 

 supposed to have been long extinct is still represented in our seas. 



Mr. Seeley observed that the buccal membrane in the recent Echinida has over- 

 lapping plates, so that if the development of the plates usually forming the re7nainder 

 of the test were arrested, forms would be obtained approaching those described in the 

 paper. He stated that in his opinion both the Echinoderm-type and the Brachiopod- 

 type have analogies with the Annelids. 



Mr. H. Woodward stated that the author of the paper had done much towards the 



